Britannica Sources used in this answer

How do scientists calculate the rate of seafloor spreading?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

World map highlighting major features of the ocean basins, including trenches, ridges, basins, and plateaus labeled throughout the Pacific, Atlantic, Indian, Southern, and Arctic Oceans. Continents are shown with shaded terrain, and prominent undersea features such as the Mid-Atlantic Ridge, Mariana Trench, and Kerguelen Plateau are marked across the map. — ocean basin Major features of the ocean basins.

Scientists calculate the rate of seafloor spreading primarily by analyzing marine magnetic anomalies. This method relies on the fact that as new oceanic crust forms and cools at a spreading centre, it becomes permanently magnetized, recording the polarity of Earth’s magnetic field at that time.1

Because the magnetic field periodically reverses, the seafloor displays a symmetrical pattern of positive and negative magnetic bands parallel to the ridge axis. By applying a known time scale of these magnetic reversals—established through dating lava flows on land—scientists can determine the age of the crust at any given distance from the ridge.21

The spreading rate is calculated by dividing the distance of a specific magnetic anomaly from the ridge crest by the age of that anomaly. Additionally, researchers use radiometric dating of rock samples and the analysis of marine sediments to further refine these age determinations and confirm the history of the ocean basin.123